Ophthalmologic manifestations of brainstem stroke syndromes
- 1 Disease Entity
- 2 Diagnosis
- 3 Management
- 4 References
Posterior circulation strokes involving the brainstem can result in subsequent ophthalmologic manifestations. Brainstem stroke syndromes are a subtype of strokes which lead to ischemia of the structures of the brainstem. The midbrain, pons, and medulla oblongata are components of the brainstem which control basic body functions such as consciousness, breathing, proprioception, heart rate, and blood pressure. The midbrain—or mesencephalon— and pons have several functions which include involvement in the afferent and efferent pupillary visual pathway. The medulla includes vestibular-otolith pathways and the ocular sympathetic pathway which can produce skew deviation, nystagmus, or Horner syndrome.
Approximately 20-25% of ischemic strokes involve the posterior circulation. The most common causes of strokes involving the posterior circulation include atherosclerosis, embolism, and dissection. The arteries supplying the posterior circulation include the innominate and subclavian arteries, the vertebral arteries in the neck, the intracranial vertebral arteries, the basilar arteries, and the posterior cerebral arteries.
Atherosclerotic occlusive disease in the proximal portion of the vertebral artery of the neck is the most common cause of strokes in the posterior ciculation. Atherosclerotic occlusion in the intracranial vertebral, basilar, and posterior cerebral arteries are also common locations of strokes involving the posterior circulation. Dissections of the posterior cerebral arteries, however, are less common.
The risks factors for posterior circulation strokes include the usual vasculopathic risk factors: smoking, hypertension, hypercholesterolemia, diabetes mellitus type II, dyslipidemia, migraines with auras, atrial fibrillation, and coronary artery disease.
The brainstem is supplied by the vertebrobasilar system, which includes the following arteries: vertebral arteries, basilar arteries, posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA), superior cerebellar artery (SCA), and labyrinthine artery.
Strokes involving the arteries supplying the brainstem can result in a variety of different ophthalmologic manifestations—such as ocular motor palsies, Collier lid retraction, ptosis, diplopia, gaze palsies, nystagmus, skew deviation, issues with accommodation, and abnormal pupillary constriction/dilation.
The neuro-ophthalmologic manifestations of strokes involving the brainstem depend on the location of the ischemic event. Thus, it is essential to understand how brainstem structures are involved in visual pathways.
The optic nerve enters the brain to innervate structures in the thalamus and brainstem. The superior colliculus is involved in the control of eye movements, and the pretectum is involved in the pupillary light reflex, vertical gaze, vertical saccades, and the convergence pathway. The paramedian pontine reticular formation of the pons is involved in the horizontal gaze circuit.
Additionally, the nuclei of the oculomotor nerve (III) and trochlear nerve (IV) are located in rostral and caudal midbrain, respectively. The nuceli of the trigeminal nerve (V), abducens nerve (VI), and facial nerve (VII) are found in the pons. The impact that posterior circulation strokes have on the eyes depends on the location of the stroke.
Strokes affecting the lateral medulla—also known as Wallenberg syndrome—can result in nystagmus, ipsilateral Horner syndrome, and cranial nerve IV and V palsies. Patients with these types of strokes almost always have vestibulocerebellar symptoms. Strokes which involve territories of the dorsal midbrain cause fixed pupils, ptosis, nystagmus, and paralysis of upward gaze and accomodation. Strokes which lead to ischemia of the pons can disrupt the horizontal gaze pathway resulting in gaze palsies. Occlusions of the distal basilar artery can lead to bilateral vision loss. Furthermore, strokes involving the posterior cerebral artery result in contralateral homonymous hemianopia secondary to occipital ischemia.
Table 1: The table summarizes a variety of brainstem stroke syndromes and their according sites of ischemic compromise, cranial nerve defects, and ophthalmologic features.
Primary prevention of strokes includes strategies such as healthy diet habits, smoking avoidance/cessation, hypertension control, physical activity, weight loss, and management of type II diabetes.
It is important to distinguish the presentation of an acute anterior circulation stroke from a posterior circulation stroke. Strokes involving the cerebellum, occipital lobe, and brainstem present with vertigo, diplopia, dysarthria, dysphagia, ataxia, and “crossed” deficits—which refer to cranial nerve deficits on one side and sensory or motor defects of the opposite side. Ophthalmologic manifestations of brainstem strokes include visual field defects, pupil abnormalities, ptosis, and cranial nerve III, IV, V, or VI palsies. These ophthalmologic aberrancies can often be detected via thorough history taking and physical examination.
A crucial step of working up a stroke is to rule out or confirm a hemorrhagic stroke. This is accomplished via a non-contrast computed tomography (CT). CT is vital since a quick diagnosis of ischemic stroke (and exclusion of intracranial bleed) can expedite the administration of tissue-type plasminogen activator (tPA). However, non-contrast CTs are less adept at detecting strokes in the posterior circulation (sensitivity of roughly 60%) compared to anterior circulation strokes (sensitivity >90%). For strokes of the posterior circulation, magnetic resonance imaging (MRI) is a superior (sensitivity >80%) modality compared to CT. Furthermore, MRI can also distinguish vascular etiologies from masses and structural injuries. Diffusion weighted imaging (DWI) on cranial MRI are particularly useful sequences for visualizing acute ischemia (restricted diffusion).
Ophthalmologic symptoms of brainstem strokes include:
- Isolated hemianopia
- or quadrantanopia
- Cortical blindness
- Collier lid retraction sign (dorsal midbrain syndrome)
- Oscillopsia (nystagmus)
- Facial or eye pain
Other clinical features that accompany strokes of the posterior circulation include vertigo, dysarthria, dysphagia, unsteadiness, ataxia, and coma. Crossed deficits are also characteristic of posterior circulation stokes. Patients can experience isolated symptoms or a combination of the mentioned clinical features depending on vascular regions affected by the stroke.
A complete 8-point eye examination can detect most of the ophthalmologic features caused by brainstem strokes. Signs such as ptosis and cranial nerve palsies can be observed via basic inspection of the patient. Moreover, an assessment of the extra-ocular movements in all 9 cardinal positions of gaze can be utilized to detect cranial nerve and gaze palsies. Visual field exams can estimate the extent of vision loss. While the physical examination is a powerful tool in neuro-ophthalmology, imaging techniques can help diagnose and localize the stroke.
Ophthalmologic signs of brainstem strokes include:
- Pupil abnormalities (anisocoria, light-near dissociation, tectal RAPD)
- Ptosis or lid retraction (Collier)
- Ocular motor palsies
- Gaze palsies and internuclear ophthalmoplegia
- Nystagmus (skew deviation, see-saw, convergence-retraction)
- Cranial nerve III, IV, VI palsies
Eyelid and pupil abnormalities:
Horner syndrome can cause ptosis, however, this will usually also be accompanied by miosis and anhidrosis. Horner syndrome is characterized by dysfunctional sympathetic innervation. Thereby, Muller’s muscle will be dysfunctional which ultimately causes a partial ptosis. Complete oculomotor palsies caused by large brainstem strokes, however, will cause a complete ptosis, a down-and-out pupil, and mydriasis. A complete ptosis is observed because the oculomotor nerve innervates the levator palpebrae muscle, which is the predominant muscle used for eyelid retraction. In Parinaud’s syndrome, the pupil is usually mid-dilated and show light-near dissociation. Lid retraction—referred to as Collier’s sign—will also be apparent in Parinaud’s syndrome.
A thorough history and physical examination can be used to diagnose strokes of the posterior circulation. Although, imaging is often utilized to assist in localizing the region of the stroke.
The first step of diagnosing a stroke is to rule out or confirm a hemorrhagic stroke. This is accomplished via a non-contrast computed tomography (CT). However, non-contrast CTs are less adept at detecting strokes in the posterior circulation (sensitivity of roughly 60%) compared to anterior circulation strokes (sensitivity >90%). For strokes of the posterior circulation, magnetic resonance imaging (MRI) with diffusion weighted imaging is a superior modality—with a sensitivity of 80-95%—compared to CT. Furthermore, MRI (especially DWI) can also distinguish vascular etiologies from masses and structural injuries.
The differential diagnosis for brainstem stroke syndromes include acute peripheral vestibular dysfunction, Meniere’s disease, intracranial hemorrhage, subarachnoid hemorrhage, malignancies, basilar migraines, toxic disturbances, osmotic demyelination syndrome, sarcoidosis, and hypoglycemia.
The first step of management in patients with acute posterior circulation strokes is to assess the airway, breathing, circulation, and to stabilize and resuscitate the patient. Once the patient is stable, the patient may be transferred and treatment may be further work-up and treatment may be initiated.
After treatment of the acute symptoms, it is important to work-up the underlying cause of the stroke. The mechanism of the stroke will affect preventative management for the patient. For example, anticoagulation will be needed in patients with atrial fibrillation.
Intravenous tissue-type plasminogen activator (tPA) can be used in patients with strokes involving the brainstem if it is administered within 4.5 hours of symptom onset. However, in cases of acute basilar occlusion, acute endovascular therapy—which involves intra-arterial clot retrieval or lysis—is performed due to the high risk of death or severe disability in the absence of recanalization. However, ongoing randomized controlled trials are currently being performed to investigate the value of early intra-arterial therapy in basilar occlusion as the indications and benefits compared to therapy with tPA are unclear.
Medical follow up
There are two main categories of vision problems that may be present after posterior circulation strokes:
- Neuromuscular impairment
- Visual processing impairment
Neuromuscular impairment occurs secondary to damage to the nerves that innervate the extraocular muscles, which leads to impaired eye coordination and diplopia. Neuromuscular impairment can be treated with extraocular muscle exercises which can strengthen and improve extraocular muscle coordination.
Visual processing impairment
There are three types of therapy modalities for visual impairment: eye movement therapy, optical therapy, and visual restoration therapy.
Eye movement therapy and optical therapy are used to treat and managed the symptoms of vision loss, while visual restoration therapy aims to improve the visual processing capability of the brain. Eye movement therapy involves strategies such as visual search, visual scanning exercises, and scanning compensatory training.
Optical therapy utilizes mirrors and prisms to enhance the user’s visual field. In cases where diplopia does not resolve, an eye patch can be used to eliminate the perception of double vision. These therapy modalities are strategies which help patients compensate and adapt to their visual impairment.
Visual restoration therapy (VRT) was a relatively new treatment modality that was reported by Sabel and colleagues. VRT employs the use of lights to stimulate the salvageable areas between the functioning regions and “blind” spots in the visual field. The theory behind the restoration therapy was that light could be used stimulate and strengthen the compromised neural pathways the are involved in visual processing. However, a study in 2005 by Reinhard and colleagues found no significant improvement in the visual defects of patients who underwent VRT. Currently, there are no therapies that can restore vision that has already been lost secondary to brainstem strokes. However, vision rehabilitation and low vision services are recommended.
Currently, there are no interventions that can resolve or reverse the neuromuscular and visual processing impairments patients have after brainstem strokes.
The prognosis of brainstem strokes are dependent on stroke severity, patient age, the degree of neurologic impairment, and the size/location of the infarction on neuroimaging with MRI or CT. The largest proportion of recovery occurs in the first three to six months after a stroke has occurred.
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